Polypropylene fiber concrete impact on the performance of the understanding:

    1. Introduction

    Polypropylene fiber is a new type of concrete reinforcing fibers, known as concrete "non-essential reinforcing ribs" for the road bridge, fabric Wall, floor and other parts of the project in recent years in China's municipal, roads and buildings the project has been more use. Since 1997, only polypropylene road and bridge projects in Tianjin in the amount of fiber reinforced concrete has reached more than ten million m2, the total amount of nearly 20 tons of polypropylene fibers, most projects use the role better.

    Since the incorporation of polypropylene fibers to improve the quality of the concrete, making use of the function of the concrete has been summarized progress, Federal Highway Strategy Programme (SHRP) After a lot of research and engineering experiments lessons learned that can be organic fibers such as polypropylene fiber reinforced concrete when as a concrete pavement high function [1]. But the authors and after construction, site planners to communicate, found that many of the effects of engineering and technical personnel of polypropylene fibers in concrete know lack of polypropylene fibers that function only hinder the onset of plastic cracking of concrete, while the function of the non-hardened concrete an active role, and perhaps enhance the role of the polypropylene fibers and steel fibers were cf ,, to incorporate fiber concrete progress on the degree of flexural (tensile) strength as the assessment specification. After analysis by the thought that the officer knew the one-sidedness of the primary functions of polypropylene fiber on the concrete to harden due to the limitations and prolonged static load strength concrete constitute existing experimental evaluation approaches for policy ideas stereotype. This article comments on the relevant questions and discusses the author's point of view.

 
    2. The effect of crack resistance of polypropylene fibers

    Comparison with conventional steel fibers, polypropylene fibers are characteristic fineness (equivalent diameter of 0.02 ~ 0.1mm), more than the number (commonly 0.9kg / m3 dosage abundant slack available 7000000 ~ 30 million monofilament ), in concrete fiber distance is small. These features can be useful polypropylene fibers bound early (pre-plastic and hardening of) concrete because segregation, bleeding, shortening and other elements constitute the primary fracture attacks and carry out, reducing the number of existing fractures and standards. The existing fractures are generally concrete damage or deterioration of the function of the source. From this point of view to understand, polypropylene fibers for crack resistance effect of the above meaning lies not only useful hampered early onset of plastic cracks of concrete and conduct, meaning that more data through a series of progressive media, enabling function of hardened concrete has been significantly improved. On pavement and bridge deck concrete, as accepted by the repeated bending and tension force sensitivity to impact loading native cracks in concrete and standard on the high number of native fissures decrease in the number and standard of right and wrong on the progress of its use function very advantageous [2].

    The existence of doubt:
① crack resistance effect of polypropylene fiber is a necessary condition to develop together concrete hardening in the deformation is limited and pre-loss condition shortened, and small specimens such conditions indoors or do not have the manufacturing site. This distinction reflects the internship with a small specimen identification internship layout objects in concrete strength or durability of the lack of the Department of polypropylene fiber reinforced concrete, this tendency is more significant. The results of polypropylene fibers forming a concrete role in the contempt.
② crack resistance effect of polypropylene fiber is still difficult to assess quantitatively through experiments. Although the officer mimic field conditions created a variety of experimental apparatus to discuss the effect of crack resistance of polypropylene fiber [3] [4], but occasionally by various elements of the role, the reproducibility of the experimental results of Qianan. Above elements formed the vague use of polypropylene fibers and to know the role of contempt on.

    Incorporation of intent fiber materials started in the concrete that is formed on due to lack of breakable doubt tensile strength of concrete, crack resistance effect on the fibers in the concrete practice of what progress has been reflected tensile strength of concrete, but not the same kind of fiber due to the elastic modulus, tensile strength, aspect ratio, etc. are not the same dosage, crack resistance in concrete effects and mechanism of action are not the same effect. Expand the crack crack resistance of steel fiber effect reflected in the obstruction of hardened concrete damage is a result of hardened concrete after cracking tensile strength must still adhere to the completion of, crack resistance effect the outcome of the role of progressive deformation of hardened concrete talent, is the concrete substrate must be insisted upon damage ductility (false ductility), and thus, resistance to cracking and fiber elastic modulus of steel fiber interfacial bond strength and tensile strength itself relevant. The primary effect of the tensile strength and crack resistance of polypropylene fibers embodied in eliminating or reducing the early onset of concrete cracks and natively carry, simple to understand can be progressed through the polypropylene fiber pre-finished concrete, further analysis of the results of the Sharpen the top polypropylene fiber stress fracture native gathering, the stress field within the media and even become more successive actions. Because early low tensile strength of concrete itself, therefore, tensile strength, elastic modulus polypropylene fibers and fiber can crack resistance target is not significant, whereas with increasing fineness of the fiber, the fiber concrete distance decreases enhanced.

    After the above analysis shows that crack resistance effect of polypropylene fibers and steel fibers not replace each other, due to improved function not leave together on concrete. Concrete bridge on the road, the effect of steel crack resistance of concrete after a split can only carry no meaning internship, and concrete in the pre-function easy to attack the shortcomings of plastic cracking but it can be resolved through the incorporation of polypropylene fibers or improvements.

    3. Impact of polypropylene fiber concrete strength

    Elastic modulus polypropylene fiber is low (about 1/10 of concrete), has a certain thickening effect and weak interfacial effects are unlucky on the strength of concrete elements [5], but because of polypropylene fibers used in concrete volume fraction is low, the impact of the above factors on the strength of concrete unlucky not significant. Many tests also indicate the results of the test piece, the incorporation of polypropylene fibers had no significant effect or the strength of concrete fell slightly on the strength of concrete. Some are accustomed to compressive or flexural strength test pieces of information to determine the function of the level of engineering and technical personnel thus concluded that: Although polypropylene fibers can hinder the early onset of plasticity of concrete cracking, but no enhancement of the hardened concrete.

    Know more widespread, and its one-sidedness that:

① small specimen strength and do not represent the strength of the layout of objects in the concrete practice, after the incorporation of polypropylene fibers when the concrete function enough this tendency even more significant because of the small specimen test results of polypropylene fibers can not show crack resistance effect brought advantages.
② concrete bridge deck pavement accept primary role in the formation of the vehicle repeated shocks tired, and thus, the strength of the anti-dynamic load can be more near to real data using the function level, and small specimens compressive or flexural strength is in the testing machine loading rate measured under quasi-static load strength. About the results of the experiment indicated [2]: Despite the incorporation of polypropylene fibers for concrete quasi-static load strength had no significant effect, but in order to make the concrete impact of anti-fatigue and can improve significantly.

    Fiber to the extent of the impact strength of concrete and fiber volume fraction in concrete related. Because quotes and technical reasons, commonly used fiber content is generally low (volume rate is generally less than 2%), and the fibers to spread chaos in the three-dimensional situation, enhanced power is very low, therefore, under normal circumstances, not to make fiber tensile strength of concrete crack before significant progress. After the concrete matrix cracking, fiber can be sustained after the bear loads. When the steel fiber content must reach levels often, fiber can bear loads exceed the level of concrete cracking in the concrete before the split, reflecting the progress of the ultimate tensile strength of concrete. And during the flexural strength test, because the concrete after cracking through fiber tensile must adhere to, so that the neutral axis of the test to progress trabecular flexural strength of concrete increases thus larger fluctuations. Test results of the general progress of the ups and downs of steel fiber concrete flexural strength of higher tensile strength. Polypropylene fiber volume content is also commonly used in much lower than that of steel fiber (0.9kg / m3 dosage equivalent volume of 0.1%), this content on the front of concrete cracking, the strength and shape of the crack damage after almost no effect , and because polypropylene fiber itself is low elastic modulus, so that even after progress FIBERS must adhere to the tensile strength of concrete after cracking, but too much to make it useful meaning deformation is small, therefore, generally do not use high content of fiber concrete progress tensile (flexural) strength polypropylene practice. Because the stiffness of the concrete bridge deck pavement demand, in fact, no matter what the progressive role of fiber strength after cracking of the concrete on the meaning of such works no internship.

    From the above analysis the conclusion is: the concrete bridge deck pavement, under normal circumstances the influence of fiber concrete static or quasi-static load carrier does not significantly affect the strength of the formation of the practice of using the function. The excellent use of the fiber concrete action to prove many engineering internship internship fiber concrete progress shock, anti-fatigue to actions, and this is the result of the incorporation of fiber integrity of the concrete slab, a series of improved results. Polypropylene fibers and steel fibers, although the same effect at this point, but the mechanism was not the same. Mechanism of polypropylene fiber is the result of eliminating or reducing the number of existing fractures and standards, so that a series of data media to progress, and organic materials to absorb impact energy to make the impact of concrete, anti-fatigue function can be improved. Polypropylene fiber itself lower elastic modulus make it load transfer to and bound to hardened concrete cracks expand relatively weak. Compare with polypropylene fiber, steel fiber because of the relatively small number in the concrete can not be useful to eliminate or reduce the number of existing fractures and standards, but higher modulus of elasticity that it has a strong ability to pass loads and constraints Cracks can expand. Above function makes steel fiber concrete pavement slab acceptable vehicle impact action can in a larger range of dispersion plate, the stress will be set to reduce the appearance of parts, concrete bridge deck pavement shock and exhaustion to obtain progress .

    The use of fiber reinforced concrete above function is unable to go through small specimens were identified and measured, but many of the engineering internship has given proof of this. Manufacturing thin Whitetopping in some US highways and airport pavement CKS choice quiz polypropylene fiber reinforced concrete, to transform the old road, is the use of polypropylene fiber reinforced concrete excellent impact resistance, anti-fatigue function [6].

    4. Effects of polypropylene fiber on the durability of concrete

    There are also some engineers think polypropylene fiber is a priority to improve the durability of concrete information. If the anti-fatigue function as a bridge deck pavement durability of concrete goals, of course, the above understanding is correct. In addition, the effect of improving the function of polypropylene fiber concrete also contains: After the bleeding cut concrete, the quality of the appearance of the concrete is improved, so that the wear resistance of concrete function to progress, as well as crack resistance effect can significantly improve anti-leakage function, etc. concrete. The durability of polypropylene fiber to other goals, such as anti-permeability of concrete, frost and salt freezing resistance, chemical resistance, also has no impact unlucky, but the degree of improvement needs further discussion.

    5. Conclusion

    After the above analysis concluded that: ① polypropylene fibers can eliminate or reduce the number of fractured concrete natively and standards, this effect is not only useful to impede the onset of plasticity of concrete cracking on function of hardened concrete is also very beneficial. ② polypropylene fibers although not hardened concrete quasi-static load strength significant progress, but after concrete progress and impact of anti-fatigue function to make use of the function of the concrete bridge deck pavement can be improved. ③ because the difference in the fiber fineness modulus of elasticity and other functions, the polypropylene fiber and steel fiber concrete influence on the function and mechanism of endless, as both have their own strengths. ④ because reason experimental evaluation approaches, indoor small specimens can use to show the role of polypropylene fiber abundant in engineering practice, the formation of polypropylene fibers internship Role in contempt.

    The direction of future research should be a composite effect of the compound effect of polypropylene fibers and steel fibers for high strength and high impact polypropylene fiber concrete utility function, the polypropylene fibers and silica fume or fly ash and other active admixture, as well as fiber Measures such as the use of the role of assessment. Discussion of fiber reinforced concrete measures should also pay more attention to the role of investigating the use of engineering practice, rather than simply through indoor small specimens function evaluation.

    Because polypropylene fiber is the result of the elimination or reduction of the number of existing fractures and standards to improve the quality of concrete to complete the concrete application of improved function, which can be incorporated into polypropylene fiber concrete as an important way to complete high function of depth discussion.